1. Field of the Invention - This invention relates to automatic gain control circuitry including a root-mean-square circuit and, more particularly, to an automatic gain control including a root-mean-square circuit for digitized audio channels in a multichannel multiplexed PCM data stream such as occurs in the digital domain conferencing bridge of a telephone network.
2. Statement of the Problem - An automatic gain control (AGC) is a term used to define a circuit and/or process for automatically obtaining a substantially constant amplitude output for an input signal having a range of variation. Numerous analog AGC circuits exist for controlling the audio output in radio and television receivers. Some analog AGC circuits use the root-mean-square (RMS) value of the input analog signal as part of the control.
A need exists for an automatic gain control incorporating an RMS circuit for use in the digital domain such as is found in a conferencing bridge of a telephone network. This is especially true in providing a circuit for controlling the gain of each digitized audio channel in a multi-channel multiplexed pulse-code-modulated (PCM) data stream. Such a control must be high speed and capable of operating at PCM data rates of 256 kilobytes per second.
3. Solution to the Problem - The present invention provides a high speed circuit and method for controlling the gain at each digitized channel in a multi-channel multiplexed PCM data stream which occurs on a conference bridge in a telephone network. The preferred embodiment controls the gain of each channel of a multichannel multiplexed PCM data stream carrying the digitized speech of the parties in a conference call. The circuit of the present invention is purely digital in operation and incorporates the use of a digital RMS meter.